Display device

Abstract: A display device such as a color phosphor display panel has a panel assembly comprising a faceplate, a pair of spaced side plates, and a backplate 1c which are joined together to provide an evacuated interior space. The display device includes a color filter layer comprising red, green, and blue filters disposed on the inner surface of the faceplate, the filter layer containing fine particles of inorganic metal compounds. A plurality of phosphor layers of ZnO : Zn are disposed on the color filter layer. A grid is disposed in spaced relation between the phosphor layers and a cathode for controlling a flow of thermions emitted from the cathode toward the phosphor layers. The fine particles of inorganic metal compounds have a particle size ranging from 0.01 µm to 0.02 µm. Preferably, the red filter contains fine particles of Fe₂O₃, the green filter contains fine particles of TiO₂·ZnO·CoO·NiO, and the blue filter contains fine particles of CoO·Al₂O₃. The phosphor layers are made of ZnO : Zn.

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a display device for use as a color phosphor display panel, for example, in a speedometer on an automobile, for example. Description of the Prior Art: There have heretofore been known color phosphor display tubes comprising a combination of a bluish green phosphor ZnO : Zn and color filters. The materials of the color filters that are used have to be thermally stable because a heat treatment process is usually carried out at about 500°C when such a color phosphor display tube is manufactured. The color filters for use in those color phosphor display tubes are thus made of inorganic materials, rather than organic materials that are used in liquid crystal display panels, for example. It is preferable that the color filters have a high transmittance so as not to reduce the intensity of light emitted from the phosphor, and also have a low reflectance. The materials that have found wide use in the art are metal colloids (see, for example, "Two-color Graphic FLVFD with Internal Color Filters" by Yoshihisa Tsuruoka & Yoshinari Okamoto, proceeding Japan Display, P1-2 (1992)). However, as shown in FIG. 1 of the accompanying drawings, red and blue filters of the conventional materials transmit light having wavelengths other than those of red and blue light. Therefore, the chromaticity points on a CIE chromaticity diagram shown in FIG. 2 of the accompanying drawings are represented by red: x/y = 0.347/0.281, bluish green: x/y = 0.235/0.405, and blue: x/y = 0.260/0.297, resulting in a narrow color reproducing range. Consequently, no satisfactory colors can be produced by the conventional color phosphor display tubes. In the US-A-4,392,077 an image display is disclosed which has a faceplate with a viewing screen including a patterned layer of phosphor particles disposed contiguous on an inner surface thereof. For minimizing loss of contrast caused by reflection of ambient light from the layer there is provided a shallow, random, clumped, discontinuous, open dispersion of contrast-enhancing particles of pigment having a body color corresponding generally to said predetermined color located directly on the faceplate beneath the layer and not significantly admixed with the phosphor particles. The particles of pigment are selected from a group consisting of cadmium sulfoselenide, iron oxide, cobalt aluminate, cobalt silica zinc and chromic oxide. OBJECTS AND SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a phosphor display device which is capable of reproducing colors in a wide color reproducing range and which allows to control a flow of thermious toward phosphor layers. According to the present invention, there is provided a display device according to the features of the appended claim 1. The fine particles of inorganic metal compounds may have a particle size ranging from 0.01 µm to 0.02 µm. The red filter may contain fine particles of Fe 2 O 3 . The green filter may contain fine particles of TiO 2 ·ZnO·CoO·NiO. The blue filter may contain fine particles of CoO·Al 2 O 3 . The display device may further comprise an indium tin oxide layer disposed between said color filter layer and said phosphor layers. The phosphor layers may be made of ZnO : Zn. The red, green, and blue filters are capable of separating red, green, and blue light more effectively from light emitted by the phosphor layers 7 than the conventional color filters. As a result, the display device can emit light of purer three primaries. Since the color filters contain fine particles of inorganic metal compounds, these fine particles do not reduce the transmittance of light passing therethrough. The above and other objects, features, and advantages of the present invention will become apparent from the following description of illustrative embodiments thereof to be read in conjunction with the accompanying drawings, in which like reference numerals represent the same or similar objects. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing transmittance characteristics of conventional color filters; FIG. 2 is a diagram illustrative of a color reproducing range of the conventional color filters on a CIE chromaticity diagram; FIG. 3A is a cross-sectional view of a front-emission phosphor display panel as a display device according to the present invention; FIG. 3B is an enlarged fragmentary cross-sectional view of a portion of the display device according to the present invention; FIG. 4 is a fragmentary perspective view of a front-emission graphic phosphor display panel according to the present invention which incorporates the principles of the display device shown in FIGS. 3A and 3B; FIG. 5A through 5I are fragmentary cross-sectional views showing a process of manufacturing the display device; FIGS. 6A through 6C are diagrams showing transmittance characteristics of filter layers of the display device; and FIG. 7 is a diagram illustrative of a color reproducing range of the color filters of the display device on a CIE chromaticity diagram. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 3A, a front-emission phosphor display panel as a display device according to the present invention includes a panel assembly 1 comprising a faceplate 1a of glass, a pair of spaced side plates 1b of glass joined at one edges thereof to the faceplate 1a, and a backplate 1c joined to opposite edges of the side plates 1b. The panel assembly 1 has an evacuated interior space which is defined by the faceplate 1a, the side plates 1b, and the back plate 1c. An electrostatic and light shield film 2 is disposed on the inner surface of the backplate 1c that faces the evacuated interior space in the panel assembly 1. The panel assembly 1 houses therein filaments 3 and a grid 4 that are successively arranged in the order named in a direction from the backplate 1c toward the faceplate 1a. The filaments 3 serve as a cathode for emitting thermions, and the grid 4, which is spaced from and disposed between the filaments 3 and the faceplate 1a, serves to control the flow of emitted thermions. A color filter layer composed of red, green, and blue filters 5R, 5G, 5B is deposited on the inner surface of the faceplate la according to a process described later on. On each of the filters 5R, 5G, 5B, there are disposed a transparent indium tin oxide (ITO) layer 6 that serves as an anode on the filter and a phosphor layer 7 on the ITO layer 6. The phosphor layer 7 is made of a phosphor ZnO : Zn which emits bluish green light. A pigment of Fe 2 O 3 is dispersed in the red filters 5R. A pigment of TiO 2 ·NiO·CoO·ZnO (1 : 1 : 1 : 1) is dispersed in the green filters 5G. A pigment of CoO·Al 2 O 3 (1 : 1) is dispersed in the blue filters 5B. These pigments should preferably have a particle size ranging from 0.01 µm to 0.02 µm for increased filter transmittance. It is well known in the art that the transmittance of a filter is increased if the size of particles dispersed in the filter is sufficiently smaller than 1/2 of the wavelength of light incident on the filter. As shown in FIG. 3B, black stripes 8 made of carbon, Fe 3 O 4 , an insulating material, for example, are interposed at predetermined spaced intervals between the faceplate 1a and the filters 5R, 5G, 5B for increasing the contrast of displayed images. Each of the filters 5R, 5G, 5B is arranged so as to lie over adjacent two of the black stripes 8. FIG. 4 shows in fragmentary perspective a front-emission graphic phosphor display panel according to the present invention which incorporates the principles of the display device shown in FIGS. 3A and 3B. As shown in FIG. 4, the front-emission graphic phosphor display panel includes a faceplate 11a, a pair of spaced side plates 11b, and a backplate 11c which are joined together providing a hermetically sealed housing 11, which is evacuated through an exhaust pipe 20 mounted on the backplate 11c. A color filter layer composed of color filters as shown in FIG. 3B is disposed on the inner surface of the faceplate 11a. A striped phosphor layer 17 which is composed of phosphor layers 17R, 17G, 17B is disposed on ITO layers (not shown) which serve as an anode that are disposed on the color filter layer. The front-emission graphic phosphor display panel also has a grid 14 in the form of closely spaced parallel wires extending perpendicularly to the striped phosphor layer 17 and spaced therefrom by a spacer 19 of glass. A plurality of filaments 13 serving as a cathode are disposed between the grid 14 and the backplate llc and extend in the same direction as the striped phosphor layer 17. The grid 14, the ITO layers, and the filaments 13 are electrically connected to external circuits by grid leads 14a, anode leads 16a, and filament leads 13a that extend respectively therefrom. A process of manufacturing the display device shown in FIGS. 3A and 3B will be described below with reference to FIGS. 5A through 5I. First, as shown in FIG. 5A, a number of parallel black stripes 8 are formed on a faceplate lc according to a known procedure. Then, as shown in FIG. 5B, the faceplate la and the black stripes 8 are coated on their entire surfaces with a PVA-ADC photosensitive liquid or an azido photosensitizer (such as of polyvinyl pyrrolidone) 21, which is thereafter dried. Areas 21G, 21B of the coated layer 21 which correspond to green and red color filters are exposed to ultraviolet radiation using a color selecting mask (not shown). Thereafter, the surface of the coated layer 21 is developed using pure water, thus removing areas 21R corresponding to red filters as shown in FIG. 5C. A suspension is prepared which is composed of 90 % of water and 10 % of a red pigment (e.g., DEFIC-R1007 (trade name) manufactured by The Dowa Mining Co. Ltd.) comprising fine particles of iron oxide (Al 2 O 3 ). The suspension is coated on the surface formed so far, and dried into a suspension layer 25 as shown in FIG. 5D. After an aqueous solution of hydrogen peroxide is sprayed over the suspension layer 25, it is developed in reverse with 10 weight % of pure water, thereby removing the photosensitizer and the pigment from those areas except the areas 25R. In this manner, red filters 5R are completed as shown in FIG. 5E. Then, the surface formed so far is coated with a PVA-ADC photosensitive liquid in which there is dispersed a blue pigment (e.g., Dyepyroxide TM blue # 3410 (trade name) manufactured by Dainichiseika Color and Chemicals Corp.) composed of fine particles of CoO·Al 2 O 3 , and the coated PVA-ADC photosensitive liquid is dried into a layer 22 as shown in FIG. 5F. Areas 22B of the layer 22 which correspond to the blue filters are exposed to ultraviolet radiation using a color selecting mask (not shown). Thereafter, the surface of the coated layer 22 is developed using pure water, thus removing the unwanted photosensitizer and the pigment. In this manner, blue filters 5B are completed in addition to the red filter 5R as shown in FIG. 5G. Subsequently, the surface formed so far is coated with a PVA-ADC photosensitive liquid in which there is dispersed a green pigment (e.g., Dyepyroxide TM blue # 3320 (trade name) manufactured by Dainichiseika Color and Chemicals Corp.) composed of fine particles of TiO 2 ·ZnO·CoO·NiO, and the coated PVA-ADC photosensitive liquid is dried into a layer 23 as shown in FIG. 5H. Areas 23G of the layer 23 which correspond to the green filters are exposed to ultraviolet radiation using a color selecting mask (not shown). Thereafter, the surface of the coated layer 23 is developed using pure water, thus removing the unwanted photosensitizer and the pigment. In this manner, green filters 5G are completed in addition to the red and blue filters 5R, 5B as shown in FIG. 5I. Then, as shown in FIG. 3B, the ITO layers 6 and the phosphor layers 7 are formed on the filters 5R, 5G, 5B. The chromaticity points of the red, green, and blue filters 5R, 5G, 5B which have different transmittances were measured, and the results are shown in FIGS. 6A through 6C, and 7 and Table 1 below. The transmittance and relative luminance without color filters was set to 100 %, and four types of color filters 5R-1 ∼ 4, 5G-1 ∼ 4, 5B-1 ∼ 4 were formed for the respective colors as shown in FIGS. 6A through 6C and Table 1. Phosphor ZnO : Zn Filter Chromaticity point Relative luminance x y 5R - 1 0.459 0.500 21 % 5R - 2 0.512 0.470 15 % 5R - 3 0.567 0.419 7 % 5R - 4 0.595 0.389 4 % 5G - 1 0.230 0.460 66 % 5G - 2 0.229 0.503 52 % 5G - 3 0.226 0.541 39 % 5G - 4 0.225 0.585 24 % 5B - 1 0.179 0.349 56 % 5B - 2 0.171 0.340 50 % 5B - 3 0.134 0.284 33 % 5B - 4 0.116 0.260 16 % No filters 0.228 0.394 100 % (Note) The relative luminance was 100 % with no color filters. As can be understood from Table 1 and FIG. 7, a highly luminous phosphor display panel having a much wider color reproducing range than conventional phosphor display panels could be achieved according to the above embodiment of the present invention. Furthermore, the contrast of displayed images can be increased according to the above embodiment of the present invention. The phosphor layers may be made of any of various other materials than ZnO : Zn. For example, phosphor layers of SnO 2 : Eu may be disposed on the red filters. The phosphor layers of SnO 2 : Eu have luminance and chromaticity that are much higher with respect to the red filters than phosphor layers of ZnO : Zn, as shown in Table 2 below. Phosphor SnO 2 : Eu Filter Chromaticity point Relative luminance x y 5R - 1 0.598 0.401 60 % 5R - 2 0.600 0.399 56 % 5R - 3 0.607 0.393 37 % 5R - 4 0.614 0.385 23 % (Note) The relative luminance was 100 % with no color filters. The principles of the present invention are not limited to the illustrated embodiment, but may be applied to cathode-ray tubes, plasma display panels, for example. According to the present invention, as described above, the display device employs color filters containing dispersed fine particles of inorganic metal compounds of Fe 2 O 3 , TiO 2 ·NiO·CoO·ZnO, or CoO·Al 2 O 3 . Therefore, the display device, particularly a color phosphor display panel, has a wide color reproducing range and a high luminance. Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments and that various changes and modifications could be effected by one skilled in the art without departing from the scope of the invention as defined in the appended claims.

Claims: A display device comprising: a faceplate (1a), a color filter layer comprising red, green, and blue filters (5A,5B,5C) disposed on said faceplate (1a), said filter layer containing fine particles of inorganic metal compounds; a plurality of phosphor layers (7) disposed on said color filter layer; a cathode (3) for emitting thermions toward said phosphor layers (7), characterized by a grid (4) in the form of closely spaced parallel wires disposed in spaced relation between said phosphor layers (7) and said cathode (3), said grid (4) being connected to an external circuit for controlling a flow of thermions emitted from said cathode (3) toward said phosphor layers (7). A display device according to claim 1, wherein said fine particles of inorganic metal compounds have a particle size ranging from 0.01 µm to 0.02 µm. A display device according to claim 1, wherein said red filter (5A) contains fine particles of Fe 2 O 3 . A display device according to claim 1, wherein said green filter (5B) contains fine particles of TiO 2 ·ZnO·CoO·NiO. A display device according to claim 1, wherein said blue filter (5C) contains fine particles of CoO·Al 2 O 3 . A display device according to claim 1, further comprising an indium tin oxide layer (6) disposed between said color filter layer and said phosphor layers (7). A display device according to claim 1, wherein said phosphor layers (7) are made of ZnO : Zn.

Inventors: KUSUNOKI TSUNEO, OHNO KATSUTOSHI, KUSUNOKI, TSUNEO, OHNO, KATSUTOSHI, KUSUNOKI, TSUNEO, C/O SONY CORPORATION, OHNO, KATSUTOSHI, C/O SONY CORPORATION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1994
Main classification: H01J29
IPC codes: H01J29, G02B5, H01J31